Snowmobile drivetrain

ABSTRACT

Methods and apparatus for propelling snowmobiles are disclosed. A snowmobile in accordance with an exemplary embodiment of the present invention comprises a chassis defining a tunnel, a drive shaft at least partially disposed in the tunnel, and at least one drive sprocket fixed to the drive shaft. A drive track overlays a portion of the at least one drive sprocket. A bearing is disposed within an interior of the drive track for rotatably supporting the drive shaft. The drive shaft is preferably operatively coupled to an engine by a drivetrain. In an advantageous embodiment, the drivetrain comprising a reduction mechanism that is substantially disposed within the tunnel defined by the chassis. In a particularly advantageous embodiment, the reduction mechanism is disposed within a projection extending from a drive sprocket fixed to the drive shaft.

RELATED APPLICATIONS

This is a Division of application Ser. No. 10/137,970 filed May 3, 2002now U.S. Pat. No. 6,755,271.

This application is related to and claims priority to U.S. ProvisionalApplication No. 60/318,151, filed Sep. 7, 2001, and entitled SnowmobileDrivetrain.

This application is also related to and claims priority to U.S.Provisional Application No. 60/317,892, filed Sep. 7, 2001, and entitledSnowmobile Providing an Enhanced Riding Experience.

The entire disclosure of the fore mentioned applications is herebyincorporated by reference.

FIELD OF THE INVENTION

The present invention relates generally to snowmobiles. Moreparticularly, the present invention relates to methods and apparatus forpropelling snowmobiles.

BACKGROUND OF THE INVENTION

Since their development in the middle of the 20^(th) century,snowmobiles have gained widespread popularity. Snowmobiles are commonlyused for trail riding and utility applications. Perhaps the most commonsnowmobile application is recreational trail riding. Trail riding on asnowmobile allows a snowmobile enthusiast to travel through areas whichare not accessible by other types of vehicles. For example, snowmobilescan travel very rapidly across frozen lakes during the winter innorthern climates. Modern snowmobiles, can cover ground very rapidly andcan cover great distances. Frequently, snowmobile enthusiasts ride theirsnowmobile for many hours straight and cover many miles.

A rider operates a snowmobile by providing inputs such as accelerationinputs provided using a throttle, deceleration inputs provided using abrake, and steering inputs provided using a set of handle bars. Therider may also influence the performance of the machine by shifting hisor her weight, for example, by leaning into a turn.

Frequently, people become interested in snowmobiling because of theunique riding experience that snowmobiles provide. Part of the thrill ofriding a snowmobile is encountering challenging terrain, and traversingthat terrain through a combination of the skill of the rider and the waythat the snowmobile reacts to the inputs provided by the rider. Aspectsof a snowmobile such as the overall weight of the snowmobile, the weightdistribution of the snowmobile, and the location of the snowmobilecenter of gravity all effect the riding experience enjoyed by asnowmobiling enthusiast.

The ability of a rider to traverse challenging terrain smoothly andquickly frequently depends upon the way that the snowmobile responds tothe rider. As mentioned previously, the rider can control the snowmobileby providing inputs using the handlebars, brake and throttle. The ridercan also control the snowmobile by selectively shifting his or herweight.

The way that a particular snowmobile responds to inputs provided by arider may depend upon the snowmobile's total inertia, the snowmobile'smoment of inertia, and the location of the snowmobile's center ofgravity. The total inertia of a snowmobile has an effect on thatsnowmobile's performance because this total inertia determines theextent to which the snowmobile will resist changes in location andlinear velocity. For example, the inertia of an overly heavy snowmobilemay limit how rapidly that snowmobile can accelerate and decelerate. Themoment of inertia of a snowmobile also has an effect on thatsnowmobile's performance, since it determines the extent to which thesnowmobile will resists changes in angular position and rotationalvelocity. The moment of inertia of a snowmobile is determine, at leastin part by the total mass of the snowmobile the way in which that massis distributed.

SUMMARY OF THE INVENTION

The present invention relates generally to snowmobiles. Moreparticularly, the present invention relates to methods and apparatus forpropelling snowmobiles. A snowmobile in accordance with an illustrativeimplementation of the present invention comprises a chassis defining atunnel, a drive shaft at least partially disposed in the tunnel, and atleast one drive sprocket fixed to the drive shaft. A drive trackoverlays a portion of the at least one drive sprocket, and an innersurface of the drive track defines an interior of the drive track.

In one aspect of the present invention, a bearing is disposed within theinterior of the drive track for rotatably supporting the drive shaft. Insome implementations of the present invention, the bearing is supportedby a housing having a first portion fixed to the chassis and a secondportion extending into the interior of the drive track. The housing maybe selectively fixed to the chassis, for example, by a plurality ofthreaded fasteners.

The drive shaft is preferably operatively coupled to an engine by adrivetrain. In one advantageous implementation, the drivetrain comprisesa reduction mechanism that is substantially disposed within the tunneldefined by the chassis. In a particularly advantageous implementation,the reduction mechanism is disposed within a projection extending from adrive sprocket fixed to the drive shaft.

In one illustrative implementation of the present invention, the speedreduction mechanism includes a first gear fixed to the drive shaft and asecond gear engaging the first gear so that a plurality of teeth of thesecond gear are intermeshed with a plurality of teeth of the first gear.The first gear advantageously has a first pitch circle that is differentfrom a second pitch circle of the second gear. The first pitch circleand the second pitch circle may be advantageously selected to provide adesired gear ratio. In certain implementations, the first gear comprisesa ring gear and the second gear comprises a spur gear disposed within acavity defined by the ring gear. In certain implementations, both thefirst gear and the second gear are disposed within a cavity defined ahousing.

In one aspect of the present invention, the speed reduction mechanism isdisposed below a reference plane defined by a top surface of the drivetrack. Placing the speed reduction mechanism in a relatively lowposition may serve to lower the center of gravity of a snowmobileincluding the speed reduction mechanism. A snowmobile with a lowercenter of gravity may be more stable and is less likely to overturn.

In an additional aspect of the present invention, a speed reductionmechanism having a compact shape is provided. In certain advantageousimplementations, the compact shape of the speed reduction mechanismallows the speed reduction mechanism to be disposed within an interiordefined by the inner surface of the drive track. In certain particularlyadvantageous implementations, the compact shape of the speed reductionmechanism allows the speed reduction mechanism to be disposed within aprojection extending from a drive sprocket coupled to the speedreduction mechanism by a drive shaft. Providing a speed reductionmechanism having a compact arrangement, and positioning this speedreduction mechanism in a central location of a snowmobile may serve toprovide a snowmobile having a reduced moment of inertia. When asnowmobile has a reduced moment of inertia the rider can more easilymake quick changes in the angular orientation and rotational velocity ofthe snowmobile.

In yet another aspect of the present invention, a speed reductionmechanism may be provided which has less rotating mass than other typesof speed reduction mechanisms. Providing a speed reduction mechanismwith a lower rotating mass serves to provide a snowmobile having quickeracceleration. Quick acceleration may be advantageous in high performanceapplications such as snowmobile racing.

In still another aspect of the present invention, a method for easilychanging the gear ratio of a speed reduction mechanism is provided. Thismethod allows a rider to change the gear ratio to tune the snowmobilefor a particular set of riding conditions. A method of changing a gearratio of a drivetrain in accordance with the present invention maycomprise the steps of 1) providing a speed reduction mechanism includinga ring gear fixed to a drive shaft, 2) providing an original assemblyfixed to the speed reduction mechanism, the original assembly includingan original drive gear rotatably supported by an original mountingplate, 3) providing a new assembly including a new drive gear rotatablysupported by a new mounting plate, the new drive gear having aneffective diameter different than an effective diameter of the originaldrive gear, 4) removing the original assembly from the speed reductionmechanism, and 5) installing the new assembly onto the speed reductionmechanism.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a snowmobile in accordance with anexemplary embodiment of the present invention.

FIG. 2 is a perspective view of a snowmobile chassis assembly inaccordance with an exemplary embodiment of the present invention.

FIG. 3 is an enlarged, perspective view illustrating a portion of thechassis assembly of the previous figure.

FIG. 4 is a perspective view of a drive assembly in accordance with anexemplary embodiment of the present invention.

FIG. 5 is an enlarged perspective view illustrating a portion of thedrive assembly of FIG. 4.

FIG. 6 is a perspective view of a speed reduction mechanism inaccordance with an additional exemplary embodiment of the presentinvention.

FIG. 7 is a plan view of a speed reduction mechanism in accordance withyet another exemplary embodiment of the present invention.

FIG. 8 is a plan view of a speed reduction mechanism in accordance withan additional exemplary embodiment of the present invention.

FIG. 9 is a cross sectional view of an assembly in accordance with anexemplary embodiment of the present invention.

FIG. 10 is a cross-sectional view of a speed reduction mechanism inaccordance with an additional exemplary embodiment of the presentinvention.

FIG. 11 is a cross-sectional view of a speed reduction mechanism inaccordance with yet another exemplary embodiment of the presentinvention.

FIG. 12 is a plan side view of a snowmobile in accordance with anexemplary embodiment of the present invention.

FIG. 13 is a diagrammatic view of a drivetrain in accordance with anexemplary embodiment of the present invention.

FIG. 14 is an additional diagrammatic view of drivetrain of FIG. 13.

FIG. 15 is yet another diagrammatic view of drivetrain of FIG. 13.

FIG. 16 is a perspective view of a snowmobile chassis assembly inaccordance with an exemplary embodiment of the present invention.

FIG. 17 is a perspective view of a snowmobile in accordance with anadditional exemplary embodiment of the present invention.

FIG. 18 is an enlarged perspective view illustrating a portion ofsnowmobile of the previous figure.

FIG. 19 is a perspective view of a cage in accordance with an exemplaryembodiment of the present invention.

FIG. 20 is a perspective view of a snowmobile in accordance with yetanother exemplary embodiment of the present invention.

DETAILED DESCRIPTION

The following detailed description should be read with reference to thedrawings, in which like elements in different drawings are numberedidentically. The drawings, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. Examples of constructions, materials, dimensions, andmanufacturing processes are provided for selected elements. All otherelements employ that which is known to those of skill in the field ofthe invention. Those skilled in the art will recognize that many of theexamples provided have suitable alternatives that can be utilized.

FIG. 1 is a perspective view of a snowmobile 100 in accordance with anexemplary embodiment of the present invention. Snowmobile 100 has achassis 102 defining a tunnel 106. In the embodiment of FIG. 1, a drivetrack 104 can be seen extending from tunnel 106. In the embodiment ofFIG. 1, drive track 104 comprises an endless loop that is supported by arear suspension 22. In a preferred embodiment, drive track 104 isoperatively coupled to an engine by a drivetrain so that drive track 104may be used to propel snowmobile 100.

In FIG. 1, it may also be appreciated that snowmobile 100 includes aplurality of skis 24. Each ski 24 is supported by a front suspension 26.In the embodiment of FIG. 1, each front suspension 26 includes atrailing arm 28 and a plurality of radius rods 30. Each front suspension26 also includes a spring assembly 32. In the embodiment of FIG. 1, eachspring assembly 32 includes a shock absorber 34 and a spring 36 that isdisposed about shock absorber 34.

FIG. 2 is a perspective view of a snowmobile chassis assembly inaccordance with an exemplary embodiment of the present invention. Theassembly of FIG. 2 includes a chassis 102 defining a tunnel 106 which ispreferably dimensioned to receive a drive track. A housing 108 definingan chamber 120 is fixed to chassis 102 in the embodiment of FIG. 2. InFIG. 2, a ring gear 122 may be seen disposed within the chamber 120 ofhousing 108. Ring gear 122 is preferably fixed to a drive shaft 124.Drive shaft 124 may be used to drive a drive track.

FIG. 3 is an enlarged, perspective view illustrating a portion of thechassis assembly of the previous figure. In FIG. 3, housing 108 can beseen extending into tunnel 106 defined by chassis 102. Also in FIG. 3,it may be appreciated that a plurality of drive sprockets 126 are fixedto drive shaft 124. A bearing 128 is shown disposed about drive shaft124 proximate one end thereof. Bearing 128 preferably rotatably supportsdrive shaft 124. Bearing 128 may be supported by a flange that isselectively fixed to the opposite side of chassis 102.

In FIG. 3, it may be appreciated that ring gear 122 is substantiallydisposed within tunnel 106 defined by chassis 102. Also with referenceto FIG. 3, it may be appreciated that housing 108 extends into tunnel106 and at least partially surrounds ring gear 122. In a preferredembodiment, housing 108 holds a bearing which rotatably supports driveshaft 124. In the embodiment of FIG. 3 housing 108 is selectively fixedto chassis 102 by a plurality of threaded fasteners 130.

FIG. 4 is a perspective view of a drive assembly in accordance with anexemplary embodiment of the present invention. The drive assembly ofFIG. 4 may be used, for example, to propel a snowmobile such as the oneillustrated in FIG. 1. In FIG. 4, the drive assembly includes a drivetrack 104 which is illustrated using phantom lines in FIG. 4. Drivetrack 104 may be driven by two drive sprockets 126 which are fixed to adrive shaft 124. The drive assembly also includes an input shaft 132. Inthe embodiment of FIG. 4, input shaft 132 and drive shaft 124 arecoupled to one another by a speed reduction mechanism 134. In apreferred embodiment, speed reduction mechanism 134 is configured toprovide a desired reduction in rotational velocity.

In FIG. 4 it may be appreciated that speed reduction mechanism 134 has acompact arrangement allowing it to fit within an interior 136 defined byan inner surface 138 of drive track 104. Providing a speed reductionmechanism having a compact arrangement, and positioning this speedreduction mechanism in a central location of a snowmobile may serve toprovide a snowmobile having a reduced moment of inertia. When asnowmobile has a reduced moment of inertia, the rider may be able tochange the angular orientation and angular velocity of the snowmobilemore quickly.

FIG. 5 is an enlarged perspective view illustrating a portion of thedrive assembly of FIG. 4. In FIG. 5 it may be appreciated that speedreduction mechanism 134 includes a ring gear 122 defining a cavity 140and a drive gear 142 disposed in cavity 140. In FIG. 5, ring gear 122 isshown fixed to drive shaft 124. Ring gear 122 has internal teeth whichintermesh with the external teeth of drive gear 142. Drive gear 142 isfixed to input shaft 132 which may be coupled to an engine of asnowmobile, for example, by a continuously variable transmission.

In FIG. 5 it may be appreciated that speed reduction mechanism 134 has acompact arrangement allowing it to fit within a projection AL extendingfrom drive sprocket 144. Speed reduction mechanism 134 of FIG. 5 mayalso have less rotating mass than other types of speed reductionmechanisms. Providing a speed reduction mechanism with a lower rotatingmass serves to provide a snowmobile having quicker acceleration. Quickacceleration may be advantageous in high performance applications suchas snowmobile racing.

FIG. 6 is a perspective view of a speed reduction mechanism 234 inaccordance with an additional exemplary embodiment of the presentinvention. In the embodiment of FIG. 6, speed reduction mechanism 234comprises a ring gear 222 that is fixed to a drive shaft 224, and adrive gear 242 that is fixed to an input shaft 232. In the embodiment ofFIG. 6, ring gear 222 includes a step 246 disposed between teeth 248 anda track surface 250. In the embodiment of FIG. 6, track surface 250 hasa diameter that is similar to a root diameter of teeth 248 of ring gear222.

In FIG. 6, two rollers 252 are shown disposed within cavity 240 of ringgear 222 in FIG. 6. In FIG. 6, it may be appreciated that rollers 252are disposed proximate track surface 250. Rollers 252 may serve tosupport ring gear 222 by selectively contacting track surface 250. It isto be appreciated that embodiments of the present invention are possiblewhich do not include rollers 252. It should also be appreciated thatembodiments of the present invention are possible which include supportelements other than rollers 252.

FIG. 7 is a plan view of a speed reduction mechanism 334 in accordancewith yet another exemplary embodiment of the present invention. Speedreduction mechanism 334 includes a ring gear 322 and an input gear 356each having a plurality of teeth. In FIG. 7, the teeth of ring gear 322and input gear 356 are illustrated having a generally rectangular shape.It is to be appreciated that gears having various tooth shapes may beused without deviating from the spirit and scope of the presentinvention. Examples of gear tooth profiles which may be suitable in someapplications include cycloidal and involute profiles.

Input gear 356 is preferably fixed to an input shaft 332. In a preferredembodiment of the present invention, input shaft 332 is rotatablysupported by a mounting plate which also supports to a plurality of pins358. In the embodiment of FIG. 7, each pin supports a roller 352including a bearing 328.

A first pitch circle 360 of input gear 356 is illustrated in FIG. 7 witha dashed line. Likewise, a second pitch circle 362 of ring gear 322 isalso illustrated with a dashed line in FIG. 7. In FIG. 7, it may beappreciated that first pitch circle 360 of input gear 356 has a diameterthat is different than the diameter of second pitch circle 362 of ringgear 322. In a preferred embodiment, the diameters of first pitch circle360 and second pitch circle 362 may be selected to provide a desiredgear ratio.

In FIG. 7, rollers 352 are shown disposed within a cavity 340 defined byring gear 322. In FIG. 7, it may be appreciated that rollers 352 aredisposed proximate a track surface 350 of ring gear 322. Rollers 352 mayserve to support ring gear 322 by selectively contacting track surface350.

FIG. 8 is a plan view of a speed reduction mechanism 434 in accordancewith an additional exemplary embodiment of the present invention. Speedreduction mechanism 434 includes a ring gear 422 defining a cavity 440.A input gear 442 is disposed within cavity 440. A support member 464 isalso disposed within cavity 440. In a preferred embodiment, supportmember 464 includes a sliding contact surface 466 having a shape similarto a track surface 450 of ring gear 422. Also in the embodiment of FIG.8, sliding contact surface 466 and track surface 450 of ring gear 422define a gap. In some embodiments of the present invention, there may bea gap between the track surface of the ring gear and sliding contactsurface 466 so that the surfaces contact one another intermittently, forexample, when the drive shaft is subjected to extreme loads. In someembodiments of the present invention, support member 464 is supported bya mounting plate that is selectively fixed to a housing.

FIG. 9 is a cross sectional view of an assembly in accordance with anexemplary embodiment of the present invention. The assembly of FIG. 9includes a chassis 502 defining a tunnel 506. A drive shaft 524 isdisposed within tunnel 506, and rotatably supported by chassis 502. Aplurality of drive sprockets 526 are fixed to drive shaft 524. A track568 is disposed at least partially within tunnel 506. In FIG. 9, track568 is shown overlaying a portion of drive sprockets 526.

An inner surface 538 of track 568 defines an interior 536. In theembodiment of FIG. 9, drive shaft 524 is rotatably supported by a firstbearing 528A that is disposed within interior 536 of track 568. In FIG.9, it may be appreciated that first bearing 528A is supported by ahousing 508 that is fixed to chassis 502. Also in FIG. 9, it may beappreciated that housing 508 extends into tunnel 506 of chassis 502 andinterior 536 of track 568.

Drive shaft 524 is also rotatably supported by a second bearing 528B. Inthe embodiment of FIG. 9, second bearing 528B is supported by a support570 that is preferably selectively fixed to chassis 502. Embodiments ofthe present invention are possible in which second bearing 528B isdisposed within interior 536 of track 568. Embodiments of the presentinvention are also possible in which drive track 504 has a width greaterthan a length of drive shaft 524.

The assembly of FIG. 9 also includes a speed reduction mechanism 534comprising a plurality of gears that are substantially disposed within achamber 520 defined by housing 508. In the embodiment of FIG. 9, speedreduction mechanism 534 comprises a ring gear 522 that is fixed to driveshaft 524, and a input gear 542 that is fixed to an input shaft 532. Inthe embodiment of FIG. 9, input shaft 532 is rotatably supported by amounting plate 572. As shown in FIG. 9, mounting plate 572 supports athird bearing 528C and a fourth bearing 528D.

Various embodiments of mounting plate 572 are possible without deviatingfrom the spirit and scope of the present invention. For example,embodiments of mounting plate 572 are possible which include a singlebearing. In the embodiment of FIG. 9, mounting plate 572 includes twobearings that are separated by a distance D. In some embodiments,distance D may effectively be zero. In other words, the two bearings maybe butted up against one another. In certain advantageous embodiments,the two bearings may be separated by a distance D which is greater thanabout zero. In certain particularly advantageous embodiments, the twobearings may be separated by a distance greater than about half thediameter of the input shaft. In these advantageous embodiments,separating third bearing 528C and fourth bearing 528D by a distanceextending along the longitudinal axis of the input shaft 532 provides ahigh level of support for input shaft 532. This advantageous arrangementprovides secure journaling of input shaft 532 by mounting plate 572.Thus, the likelihood that input shaft 532 will be free to wobble issignificantly reduced.

In the embodiment of FIG. 9, mounting plate 572 is selectively fixed tohousing 508 by a plurality of threaded fasteners 530. Housing 508 ispreferably selectively fixed to chassis 502, for example, with aplurality of threaded fasteners. Embodiments of the present inventionare also possible in which mounting plate 572 is directly fixed tochassis 502. In FIG. 9, it may be appreciated that a driven pulley 574is fixed to input shaft 532 proximate one end thereof. Driven pulley 574may form part of a continuously variable transmission.

FIG. 10 is a cross-sectional view of a speed reduction mechanism 634 inaccordance with an additional exemplary embodiment of the presentinvention. Speed reduction mechanism 634 includes a ring gear 622defining a cavity 640. Speed reduction mechanism 634 also includes ainput gear 642 which is disposed in cavity 640 defined by ring gear 622.

In FIG. 10, it may be appreciated that input gear 642 is fixed to aninput shaft 632 which extends through a mounting plate 672. As shown inFIG. 10, mounting plate 672 supports a plurality of bearings 628 forrotatably supporting input shaft 632. In FIG. 10, it may be appreciatedthat ring gear 622 is fixed to a drive shaft 624. Drive shaft 624 isrotatably supported by a first bearing 628A. First bearing 628A issupported by a housing 608. In the embodiment of FIG. 10, mounting plate672 is fixed to housing 608 by a plurality of fasteners 630. In FIG. 10,it may be appreciated that housing 608 and mount plate 678 define achamber 620. In FIG. 10, it may also be appreciated that ring gear 622and input gear 642 are disposed in chamber 620.

In the embodiment of FIG. 10, speed reduction mechanism 634 includes asupport ring 680 which is disposed within chamber 620 defined by housing608. Support ring 680 may be fixed to housing 608, for example, by pressfitting support ring 680 into chamber 620. In the embodiment of FIG. 10,a small gap exits between an inner surface of support ring 680 and outersurface 682 of ring gear 622. In a preferred embodiment, this gap isdimensioned so that outer surface 682 of ring gear 622 can contactsupport ring 680 when drive shaft 624 is subjected to extreme loads.

Support ring 680 may comprise various materials without deviating fromthe spirit and scope of the present invention. Examples of materialswhich may be suitable in some applications include bronze, sinteredbronze, and polytetrafluoroethylene (PTFE) coated steel.

FIG. 11 is a cross-sectional view of a speed reduction mechanism 734 inaccordance with yet another exemplary embodiment of the presentinvention. In the embodiment of FIG. 11, speed reduction mechanism 734includes a ring gear 722 having a plurality of teeth 748. Ring gear 722also includes a step 746 disposed between teeth 748 and a track surface750. In the embodiment of FIG. 11, track surface 750 has a diameter thatis slightly larger than a root diameter of teeth 748 of ring gear 722.In the embodiment of FIG. 11, speed reduction mechanism 734 includes aroller 752 that is disposed proximate track surface 750. Roller 752 issupported by a bearing 728 and a pin 784. Pin 784 is fixed to a mountingplate 772 for example using a friction fit. In FIG. 11, a small gap isshown between track surface 750 of ring gear 722 and the outer surfaceof roller 752. In a preferred embodiment, this gap is dimensioned sothat track surface 750 of ring gear 722 can contact roller 752 whendrive shaft 724 is subjected to extreme loads.

FIG. 12 is a plan side view of a snowmobile 800 in accordance with anexemplary embodiment of the present invention. Snowmobile 800 includes adrive track 804 which may be used to propel snowmobile 800. An engine886 of snowmobile 800 is operatively coupled to drive track 804 by adrivetrain 888 of snowmobile 800.

In the embodiment of FIG. 12, drivetrain 888 includes a drive clutch 890that is coupled to a crankshaft 892 of engine 886. Drive clutch 890 iscoupled to a driven clutch 894 by a belt 896. Driven clutch 894 is fixedto an input shaft 832 of a speed reduction mechanism 834. Speedreduction mechanism 834 is coupled to a drive shaft assembly including adrive shaft 824 and a drive sprocket 844 having a plurality ofprotrusions 898 that are adapted to mate with drive track 804. In apreferred embodiment, speed reduction mechanism 834 is disposed within atunnel 806 defined by a chassis 802 of snowmobile 800. In FIG. 12 it maybe appreciated that the axis of rotation of driven clutch 894 and inputshaft 832 is located above and forward of the axis of rotation of driveshaft 824. It is to be appreciated that other embodiments are possiblewithout deviating from the spirit and scope of the present invention. Insome embodiments, for example, the axis of rotation of driven clutch 894and input shaft 832 may be located directly above the axis of rotationof drive shaft 824. In other embodiments, for example, the axis ofrotation of driven clutch 894 and input shaft 832 may be locateddirectly above and rearward of the axis of rotation of drive shaft 824.

In FIG. 12, it may be appreciated that speed reduction mechanism 834 isdisposed below a reference plane P defined by an outer surface of drivetrack 804. Placing speed reduction mechanism 834 in a relatively lowposition may serve to lower the center of gravity of a snowmobile 800. Asnowmobile with a lower center of gravity may be more stable and is lesslikely to overturn.

FIG. 13 is a diagrammatic view of a drivetrain 888 in accordance with anexemplary embodiment of the present invention. Drivetrain 888 may beused to operatively couple an engine 886 to a drive track 804. In FIG.13, drive track 804 is illustrated using phantom lines. Drivetrain 888includes a drive sprocket 844 having a plurality of protrusions 898 thatare adapted to mate with drive track 804. Drive sprocket 844 is fixed toa drive shaft 824. A ring gear 822 is also fixed to drive shaft 824.Ring gear 822 forms part of a speed reduction mechanism 834. Speedreduction mechanism 834 also includes a first drive gear 842A and aplurality of rollers 852. First drive gear 842A is fixed to a firstinput shaft 832A of speed reduction mechanism 834. A driven clutch 894is also fixed to first input shaft 832A. A belt 896 extends betweendriven clutch 894 and a drive clutch 890. Drive clutch 890 is fixed to acrankshaft 892 of engine 886. In FIG. 13 it may be appreciated that theaxis of rotation of driven clutch 894 and input shaft 832A is locatedabove the axis of rotation of drive shaft 824 providing an elevatedposition for driven clutch 894.

FIG. 14 is an additional diagrammatic view of drivetrain 888 of theprevious figure. In FIG. 14 it may be appreciated that the center offirst input shaft 832A lies on a radius line 803 that is disposed at aradius R from crankshaft 892. In FIG. 14 it may also be appreciated thatfirst drive gear 842A has a first diameter 805A.

FIG. 15 is yet another diagrammatic view of drivetrain 888 of FIG. 13.In the embodiment of FIG. 15, first drive gear 842A has been replacedwith a second drive gear 842B. In FIG. 15, it may be appreciated thatsecond drive gear 842B has a second diameter 805B. In a preferredembodiment, second diameter 805B of second drive gear 842B is differentfrom first diameter 805A of first drive gear 842A. In this preferredembodiment, a gear ratio of speed reduction mechanism 834 may be changedby replacing first drive gear 842A with second drive gear 842B.

Second drive gear 842B is coupled to a second input shaft 832B. In FIG.15, it may be appreciated that the center of second input shaft 832Blies on radius line 803. In a preferred embodiment of the presentinvention, the same drive belt 896 can be used in the embodiment of FIG.15 and the embodiment of FIG. 14, since in both cases, the input shaftlies a distance R from crankshaft 892.

A method of changing a gear ratio of a drivetrain in accordance with thepresent invention may comprise the steps of 1) providing a speedreduction mechanism including a ring gear fixed to a drive shaft, 2)providing an original assembly fixed to the speed reduction mechanism,the original assembly including an original drive gear rotatablysupported by an original mounting plate, 3) providing a new assemblyincluding a new drive gear rotatably supported by a new mounting plate,the new drive gear having an effective diameter different than aneffective diameter of the original drive gear, 4) removing the originalassembly from the speed reduction mechanism, and 5) installing the newassembly onto the speed reduction mechanism.

FIG. 16 is a perspective view of a snowmobile chassis assembly inaccordance with an exemplary embodiment of the present invention. Theassembly of FIG. 16 includes an engine 986 that is coupled to a chassis902 defining a tunnel 906. Engine 986 is preferably coupled to a drivetrack by a drivetrain 988 for propelling a snowmobile in accordance withthe present invention. In FIG. 16 it may be appreciated that drivetrain988 includes a drive clutch 990 that is coupled to a crankshaft 992 ofengine 986. Drive clutch 990 is coupled to a driven clutch 994 by a belt996. Driven clutch 994 is fixed to an input shaft 932 of a speedreduction mechanism 934.

The assembly of FIG. 16 also includes a cage 909 that is fixed tochassis 902. Cage 909 defines a foot well 923 which is preferablydimensioned to receive the foot of a rider. In FIG. 16 it may beappreciated that cage 909 is disposed proximate driven clutch 994. Cage909 of FIG. 16 includes a wall 925 which is disposed between foot well923 and driven clutch 994.

Engine 986 of FIG. 16 includes a plurality of input ports 927. Airentering engine 986 may flow through input ports 927. Exhaust gases mayexit engine 986 via a plurality of exhaust ports 929. In the embodimentof FIG. 16, input ports 927 and exhaust ports 929 are both disposed onthe same side of a plane defined by the cylinder bore axes of engine986. In FIG. 16 it may be appreciated that engine 986 is generallydisposed at an angle relative to vertical so that the cylinder bore axesof engine 986 extend generally upwardly and rearwardly.

FIG. 17 is a perspective view of a snowmobile 1000 in accordance with anadditional exemplary embodiment of the present invention. Snowmobile1000 has a chassis 1002 defining a tunnel 1006. In the embodiment ofFIG. 17, a drive track 1004 can be seen extending from tunnel 1006. Inthe embodiment of FIG. 17, drive track 1004 comprises an endless loopthat is supported by a rear suspension 22. In a preferred embodiment,drive track 1004 is operatively coupled to an engine by a drivetrain sothat drive track 1004 may be used to propel snowmobile 1000. In someembodiments, the drivetrain of snowmobile 1000 includes a driven clutchthat is coupled to a drive clutch by a belt.

In FIG. 17, it may be appreciated that snowmobile 1000 includes a footwell 1023 that is defined by a cage 1009. Cage 1009 of FIG. 17 includesa wall 1025. In a preferred embodiment, wall 1025 of cage 1009 isdisposed between foot well 1023 and a driven clutch of snowmobile 1000.Also in a preferred embodiment, cage 1009 is selectively fixed tosnowmobile 1000 so that it can be removed, for example, when performingmaintenance on snowmobile 1000.

Snowmobile 1000 of FIG. 17 also includes a cowling 1033 defining anengine compartment 1035. In the embodiment of FIG. 17, cowling 1033includes a pan portion 1037 and a hood portion 1039. In FIG. 17, it maybe appreciated that foot well 1023 defined by cage 1009 extends into theengine compartment 1035 defined by cowling 1033. In a preferredembodiment, foot well 1023 is dimensioned to receive a foot of a rider.Also in the embodiment of FIG. 17, cowling 1033 defines a first notch1043A and a second notch 1043B. In a preferred embodiment, first notch1043A and second notch 1043B are dimensioned to receive the knees of therider. In FIG. 17, it may be appreciated that first notch 1043A isgenerally disposed above foot well 1023. In some embodiments, firstnotch 1043A is disposed above a driven clutch of snowmobile 1000. Insome embodiments, snowmobile 1000 may include a second foot well locatedbelow second notch 1043B.

FIG. 18 is an enlarged perspective view illustrating a portion ofsnowmobile 1000 of the previous figure. In FIG. 18, it may beappreciated that cage 1009 is selectively fixed to snowmobile 1000 by aplurality of threaded fasteners 1030. In FIG. 18, wall 1025 of cage 1009is shown extending at an angle relative to a longitudinal axis ofsnowmobile 1000. Cage 1009 of FIG. 18 includes a plurality of throughholes 1047 which are in fluid communication with both foot well 1023 andengine compartment 1035 of snowmobile 1000.

FIG. 19 is a perspective view of a cage 1109 in accordance with anexemplary embodiment of the present invention. Cage 1109 includes a wall1125 which partially defines a foot well 1123. In the embodiment of FIG.19, cage 1109 includes a plurality of mounting holes 1157 and aplurality of through holes 1147.

FIG. 20 is a perspective view of a snowmobile 1200 in accordance withyet another exemplary embodiment of the present invention. Snowmobile1200 of FIG. 20 includes a cowling 1233 defining an engine compartment1235. In the embodiment of FIG. 20, cowling 1233 includes a pan portion1237 and a hood portion 1239. In FIG. 20, it may be appreciated thatcowling 1233 defines a foot well 1223. In a preferred embodiment, footwell 1223 is dimensioned to receive a foot of a rider. Also in theembodiment of FIG. 20, cowling 1233 defines a notch 1249. In a preferredembodiment, notch 1249 is dimensioned to receive the knee of the rider.In FIG. 20, it may be appreciated that notch 1249 is generally disposedabove foot well 1223. In some embodiments, notch 1249 is disposed abovea driven clutch of snowmobile 1200.

Several forms of invention have been shown and described, and otherforms will now be apparent to those skilled in art. It will beunderstood that embodiments shown in drawings and described above aremerely for illustrative purposes, and are not intended to limit thescope of invention defined claims which follow.

1. A method of changing a gear ratio of a snowmobile drivetrain,comprising the steps of: providing a speed reduction mechanism includinga driven gear fixed to a drive shaft and a first assembly including afirst drive gear fixed to a first input shaft that is rotatablysupported by a first mounting plate; the first drive gear and the drivengear cooperating to provide a first gear ratio; removing the firstassembly from the speed reduction mechanism; mating a second assembly tothe speed reduction mechanism, the second assembly including a seconddrive gear fixed to a second input shaft that is rotatably supported bya second mounting plate; and wherein the second drive gear and thedriven gear cooperate to provide a second gear ratio different from thefirst gear ratio.
 2. The method of claim 1, wherein the driven gearcomprises a ring gear and the first drive gear comprises a spur gearhaving a first pitch circle diameter.
 3. The method of claim 2, whereinthe second drive gear comprises a spur gear having a second pitch circlediameter different from the first pitch circle diameter.
 4. The methodof claim 1, wherein the first input shaft of the first assembly iscoupled to a driven clutch before the first assembly is removed from thespeed reduction mechanism; and the second input shaft of the secondassembly is coupled to the driven clutch after the first assembly isremoved and the second assembly is mated to the speed reductionmechanism; the driven clutch being coupled to a drive clutch via a belt.5. The method of claim 1, wherein axes of rotation of the first andsecond input shafts are located above an axis of rotation of the driveshaft.
 6. A method of changing a gear ratio of a snowmobile drivetrain,comprising the steps of: providing an engine including a crank shafthaving an axis of rotation; providing a speed reduction mechanismincluding a driven gear fixed to a drive shaft and a first assemblyincluding a first drive gear fixed to a first input shaft that isrotatably supported by a first mounting plate; the first mounting platebeing dimensioned so that the first input shaft has an axis of rotationdisposed at a selected radial distance from the axis of rotation of thecrankshaft; removing the first assembly from the speed reductionmechanism; mating a second assembly to the speed reduction mechanism,the second assembly including a second drive gear fixed to a secondinput shaft that is rotatably supported by a second mounting plate; andthe second mounting plate being dimensioned so that the second inputshaft has an axis of rotation disposed at the selected radial distancefrom the axis of rotation of the crankshaft so that a common drive beltcan be used with both the first assembly and the second assembly.
 7. Themethod of claim 6, further including the step of providing a drivenclutch fixed to the first input shaft, a drive clutch fixed to thecrankshaft of the engine, and a drive belt coupling the driven clutch tothe drive clutch.
 8. The method of claim 7, further including the stepof removing the driven clutch from the first input shaft.
 9. The methodof claim 8, further including the step of fixing the driven clutch tothe second input shaft.
 10. The method of claim 9, further including thestep of reinstalling the drive belt so as to couple the driven clutch tothe drive clutch.
 11. The method of claim 6, wherein the driven gearcomprises a ring gear and the first drive gear comprises a spur gearhaving a first pitch circle diameter.
 12. The method of claim 11,wherein the second drive gear comprises a spur gear having a secondpitch circle diameter different from the first pitch circle diameter.13. The method of claim 6, wherein the axes of rotation of the first andsecond input shafts are located above an axis of rotation of the driveshaft.
 14. A method of changing a gear ratio of a snowmobile drivetrain,the method comprising: removing a first drive gear, a first input shaftand a first mounting plate from a speed reduction mechanism in which thefirst drive gear directly engaged teeth of a ring gear fixed to a driveshaft, the first drive gear being fixed to the first input shaft that isrotatably supported by the first mounting plate; and installing a seconddrive gear, a second input shaft and a second mounting plate into thespeed reduction mechanism so that the second drive gear directly engagesthe teeth of the ring gear, the second drive gear being fixed to thesecond input shaft that is rotatably supported by the second mountingplate.
 15. The method of claim 14, wherein the first input shaft iscoupled to a driven clutch before being removed from the speed reductionmechanism; and the second input shaft is coupled to the driven clutchafter being installed into the speed reduction mechanism; the drivenclutch being coupled, via a belt, to a drive clutch, which is coupled toa crankshaft.
 16. The method of claim 14, wherein an axis of rotation ofthe first input shaft, before being removed from the speed reductionmechanism, and an axis of rotation of the second input shaft, afterbeing installed into the speed reduction mechanism, are both disposed ata same radial distance from an axis of rotation of a crank shaft. 17.The method of claim 14, further comprising: removing a driven clutchfrom the first input shaft; and fixing the driven clutch to the secondinput shaft.
 18. The method of claim 14, wherein a drive sprocket isfixed to the drive shaft, the drive sprocket mating with a drive track.19. The method of claim 14, wherein an axis of rotation of the firstinput shaft is located above an axis of rotation of the drive shaftbefore removing the first input shaft and an axes of rotation of thesecond input shaft is located above an axis of rotation of the driveshaft after installing the second input shaft.
 20. The method of claim14, wherein the ring gear includes a track surface in proximity to aplurality of rollers.